Structural Influence on the Photochromic Response of a Series of Ruthenium Mononitrosyl Complexes

Abstract

In mononitrosyl complexes of transition metals two long-lived metastable states corresponding to linkage isomers of the nitrosyl ligand can be induced by irradiation with appropriate wavelengths. Upon irradiation, the N-bound nitrosyl ligand (ground state, GS) turns into two different conformations: isonitrosyl O bound for the metastable state 1 (MS1) and a side-on nitrosyl conformation for the metastable state 2 (MS2). Structural and spectroscopic investigations on [RuCl(NO)py(4)](PF(6))(2)·1/2H(2)O (py = pyridine) reveal a nearly 100% conversion from GS to MS1. In order to identify the factors which lead to this outstanding photochromic response we study in this work the influence of counteranions, trans ligands to the NO and equatorial ligands on the conversion efficiency: [RuX(NO)py(4)]Y(2)·nH(2)O (X = Cl and Y = PF(6)(-) (1), BF(4)(-) (2), Br(-)(3), Cl(-) (4); X = Br and Y = PF(6)(-) (5), BF(4)(-) (6), Br(-)(7)) and [RuCl(NO)bpy(2)](PF(6))(2) (8), [RuCl(2)(NO)tpy](PF(6)) (9), and [Ru(H(2)O)(NO)bpy(2)](PF(6))(3) (10) (bpy = 2,2'-bipyridine; tpy = 2,2':6',2"-terpyridine). Structural and infrared spectroscopic investigations show that the shorter the distance between the counterion and the NO ligand the higher the population of the photoinduced metastable linkage isomers. DFT calculations have been performed to confirm the influence of the counterions. Additionally, we found that the lower the donating character of the ligand trans to NO the higher the photoconversion yield.

The impact of hydrogen bonding on 100% photo-switching in solid-state nitro–nitrito linkage isomers

“…There has been a prior assumption that, for each crystal system, there is a fixed overall level of achievable MS occupation, bound either by the steric properties of the crystal or the electronic properties of the active molecule. 4,8,32,33 This study challenges that supposition, and the observation of temperature-regulated photo-activation adds a new dimension of control for single-crystal-to-single-crystal linkage isomer transformations, which may be exploited in future device technologies. Importantly, in terms of crystal engineering, the inclusion of hydrogen bond donor groups need not be avoided, a factor that will assist in the targeted design of new linkage isomer systems aimed towards specific photoswitching applications.…”

“…1 Photo-switching between linkage isomers can be achieved in both solution and the solid-state, with irradiation of the solid leading to the production of a metastable state (MS) isomer below some critical temperature. 2 In situ photocrystallographic studies have to-date revealed the structures of various MS linkage isomers, including nitrosyl, 3,4 nitrite, [5][6][7][8] sulfur dioxide, [9][10][11] and di-nitrogen 12 systems.…”

Monitoring photo-induced population dynamics in metastable linkage isomer crystals: a crystallographic kinetic study of [Pd(Bu4dien)NO2]BPh4

“…49,50 Previous studies have highlighted the influence that the surrounding crystalline environment can have on the progress of the photoreaction. 9,20,51 Intermolecular interactions involving the isomerising ligand are particularly influential, as these must be broken and/or (re)formed to facilitate the atomic rearrangements necessary for photoswitching to occur. Our recent work has highlighted the important effect that hydrogen bonding to the nitrite ligand can have on the nitro " nitrito process, 19,51 leading us to consider how intermolecular interactions can influence the photoswitching kinetics in 1.…”

“…The earliest photocrystallographic studies with linkage isomers were carried out on metal-nitrosyl complexes, including seminal work by Coppens et al on sodium nitroprusside. 5 Since then, several linkage isomer switches have been studied using photocrystallographic methods, including nitrosyl, [6][7][8][9] sulfur dioxide [10][11][12][13] and nitrite [14][15][16][17][18][19] compounds.…”

cis-Chloridobis(4,4′-dimethyl-2,2′-bipyridine)nitrosylruthenium(II) bis(hexafluorophosphate)

“…Ruthenium nitrosyl complexes can either induce photochromism (Schaniel et al, 2007b) or NO photorelease (Rose & Mascharak, 2008). In the first case, photoisomerization along the rutheniumnitrosyl bond (Ru-NO/Ru-ON) is observed in the solid state when the compounds are irradiated in the blue region (Schaniel et al, 2007a;Cormary et al, 2009Cormary et al, , 2012. It offers technological applications as optical high-capacity storage devices (Imlau et al, 1999).…”